The present invention relates to a fuel feeding apparatus for internal combustion engines such as automotive engines and, more particularly, to a fuel feeding apparatus having an electronic controller for controlling fuel feeding rate.
A typical known fuel feeding apparatus for internal combustion engines has a fuel injection portion constituted by an electromagnetic valve and disposed in the air-intake passage at the upstream side of the throttle valve and an air flow meter for detecting the air flow rate and disposed in the air-intake passage. In operation, the fuel is injected into the air-intake passage intermittently through a control of the width of the valve opening pulse for actuating the electromagnetic valve in accordance with an air flow rate signal derived from the air flow meter.
This type of fuel feeding apparatus, however, tends to suffer from a lack of uniformity of the mixture due to the intermittent fuel injection. In addition, a high accuracy of the air flow meter, as well as a complication of signal processing circuit connected to the air flow meter, is required to permit the direct detection of the air flow rate by the air flow meter.
As a measure for overcoming the above-described problems of the prior art, in, for example, U.S. Pat. No. 4,442,818, a fuel feeding apparatus is proposed wherein an air flow meter is disposed by a bypass air passage detouring the air intake passage for enabling a sensing of a change in the air flow rate.
In this proposed fuel feeding apparatus, the flow rate of air flowing through the bypass air passage is controlled by a air metering valve at a substantially constant level through a feedback of the output signal from the air flow meter. Simultaneously, the fuel feeding rate is controlled by a proportional type electromagnetic device which drives the air metering valve. This fuel feeding apparatus advantageously ensures a high response characteristics of the fuel feeding because the fuel feeding rate is automatically controlled in response to a change in the air flow rate by the proportional type electromagnetic device.
On the other hand, however, this fuel feeding apparatus leaves room for improvement in the following respect. Namely, when the air flow meter is constituted by a heat-type flow meter which produces an electric output corresponding to the heat carried away from a heat-sensitive resistor in accordance with the air flow rate, the flow rate of air is measured out only for the air flowing forwardly but also for the air flowing backwardly. Therefore, in the event that the intake air flow is a pulsating one involving a backward flow as in the case of heavy load operation, e.g. low-speed fuel-throttle operation of the engine, the output signal derived from this air flow meter is considerably greater than the signal corresponding to the actual intake air flow rate. Therefore, it is often experienced that the air-fuel ratio of the mixture actually supplied largely deviates from the set air-fuel ratio during heavy load operation of the engine. Hitherto, no effective measures has been proposed for avoiding this problem.